QUANTITATIVE ESTIMATION .nto which short, narrow glass tubes are inserted. Attach one snd of the tube to an apparatus for evolving carbon dioxide, ivhich is thoroughly dried by passing it through concentrated sulphuric acid. When the air is expelled from the tube, heat it gently until the alcohol is removed. Then let the tube cool while the gas is passing through. The spiral is then removed ind placed in the front of the combustion tube. The combustion is carried out in the manner already described, but a current of lir is substituted for oxygen until all the hydrogen has been expelled, z>., until water ceases to condense in the front of the :ube. The burners under the metallic copper are then gradually 2xtinquished, and the spiral allowed to cool whilst the current D£ air is replaced by oxygen. By the time the oxygen reaches :he spiral, the latter should have so far cooled that it remains anoxidised. The current of oxygen is continued until a glowing :hip is kindled at the end of the potash apparatus and the operation is completed by turning on the air as previously described. A convenient substance to use for analysis is acetanilide, see Preparation 54, p. 151. Combustion of Organic Compounds containing Halogens and Sulphur.—When the halogens or sulphur are present in an organic compound, they are liable to be ab- sorbed either in the free state or in combination with oxygen in the potash apparatus. In this case, fused lead chromate broken up into small pieces must replace the coarse copper oxide in the combustion tube. The halogens and sulphur are retained by the lead, the former as the halide salt, and the latter as lead sulphate Special care must be taken in using lead chromate, that the temperature of the furnace is not too high, as otherwise the chromate fuses to the glass, and the combustion tube then cracks on cooling. Nitrogen (Dumas).—According to this method, a weighed quantity of the substance is heated with copper oxide in a tube filled with carbon, dioxide. The carbon and hydrogen form respectively carbon dioxide and water, and the nitrogen which is liberated in the form of gas is collected over caustic potash (which absorbs the carbon dioxide) and measured. The following apparatus-is required :— l. A combustion furnace of the ordinary form.